It could be the most expensive bottle of asti spumante you'll ever buy. Ryanair has confirmed passengers will be charged £30 if they cannot fit their duty free purchases into their single piece of hand luggage.

The low-cost carrier, which makes sizeable profits from its add-on fees, said it would make no exceptions to its carry-on bag allowance that limits passengers to one piece of luggage. Industry observers said the move could be a blow to the dozens of small airports around Europe that rely on retailing profits to subsidise their cut-price deals with Ryanair, which drives a hard bargain with any airport that takes its planes.

Ryanair defended the charge, which it said "ensured fairness to all passengers". The airline was not the first carrier to enforce check-in fees and extra baggage charges, but it has pursued them vigorously to drive down baggage handling costs.

A Ryanair spokesperson said the £30 charge was introduced to stop blatant flouting of hand luggage rules which, the airline claims, has seen one passenger attempt to board with five pieces of hand luggage. The Ryanair chief executive, Michael O'Leary, has admitted that the airline cannot eliminate hand luggage entirely but justifies the extra charges as "behavioural" because lower baggage handling costs would ultimately lead to lower fares.

However, one industry consultant warned that regional airports might be damaged by the move. "It will dissuade people from buying duty free. It could impact airports that are dependent on people spending at their shops. You are eating into an airport's ability to generate revenues when low-cost carriers want lower fees from them," said Chris Tarry, chairman of the CTAIRA consultancy.

Under the hand luggage rules, any passenger who attempts to board with more than one piece of hand lugage will be charged £30 at the departure gate. If they refuse to pay the extra fee, they have the option of dumping their purchases at the gate or missing their flight. The hand luggage weight limit is 10kg, with maximum dimensions of 55cm x 40cm x 20cm. As well as duty free purchases, laptops and handbags will have to be contained in the single piece of hand luggage to avoid the fee.